1. Technical Field
The present disclosure relates to a method of detecting a lift amount of a valve.
2. Description of Related Art
In an engine of a vehicle, the amount of air to be taken into the engine is controlled by a throttle valve to adjust the output from the engine. Thus, in a low-load region, the throttle valve tends to be closed and the ratio of pumping loss due to suction of air is increased. In view of this, there is Valvematic that is a mechanism configured to continuously vary the lift amount of an intake valve to cause the intake valve to function as a throttle valve. With this configuration, the efficiency and fuel economy are enhanced by decreasing the intake loss.
In the inspection of the Valvematic, the lift, amount (upward-downward travel amount; opening-closing amount) of the valve is periodically measured in a state in which the engine has been assembled.
In this measurement method, for example, an eddy-current non-contact sensor (gap sensor) is provided in an engine, and an upward-downward travel amount of a retainer attached to a valve is measured by the non-contact sensor. Japanese Patent Application Publication No. 2007-303849 (JP 2007-303849 A) describes a valve lift characteristic detection apparatus configured to measure a lift amount of an upper surface of a retainer by using an eddy-current sensor, thereby detecting valve lift characteristics of a valve.
In accordance with the current trend towards downsizing of an engine, reduction in weight of a valve spring has been promoted as part of shape modifications of a space in a cylinder head and parts. A so-called beehive spring has been employed as a valve spring.
More specifically, an increase in load at the time of maximum compression of a valve spring, which is a compression coil, (load at the time when an engine valve is fully opened) may lead to an increase in friction, abrasion, and the like, in an engine, and may cause deterioration in fuel economy. In view of this, the above-described beehive spring having a lower mass is employed as a valve spring that is one of movable parts in the engine, as a measure for reducing a load at the time of maximum compression of the valve spring without a decrease in rotation limit of the engine.
In such a beehive spring, the coil diameter on the retainer side is made smaller than that on the other side. This configuration allows reduction in size and weight of a retainer that is a movable part.
Although reduction in size of a retainer leads to enhancement of fuel economy of an engine, reduction in size of the retainer makes it difficult to measure an upward-downward travel amount of the retainer by using a non-contact sensor. This makes it difficult to perform the inspection of the Valvematic.